Data transmission is becoming increasingly common, and data is being transferred for more reasons and in more ways than ever before. In the context of the present invention, data are bits of information required to perform a task of some kind in an electronic device. Data transmission refers to the transfer of this information from one device (or component of a device) to another.
Traditionally, computers have stored data, whether input manually by human operators or automatically collected in some fashion, to be able to produce reports, make calculations, or simply to store information for later reference. Data may also be processed to produce more sophisticated presentations—audio, video, or “multi-media”—or to operate mechanical devices through a proper interface.
The reason for wanting to transmit data should be apparent. Data collected in one place, or in many places, may be sent to another location for safekeeping or to perform a task there. Or the data may simply be used for personal communication, as occurs with email. The human voice (and other sounds) can, in fact, be converted into transmittable data as well. Note that while data information and voice information are often treated separately because they impose somewhat different demands on a transmission channel, for purposes of describing the present invention, “data transmission” will be used to describe the sending of any type of information content unless a distinction is explicitly stated or apparent from the context.
The current popularity of data transmission has been promoted by a variety of interconnected phenomena. One factor naturally is the widespread availability of computing devices to the general public. These devices may take the form of personal computers, cell phones, personal digital assistants, and so forth. Correspondingly, the amount of information available for transmission has increased. This includes not only the personal correspondence (such as email) mentioned above, but a wealth of text, graphics, and other types of files that can be requested by a user and returned in a very short period of time. The World Wide Web, in particular, makes a vast quantity of such information available. Finally, as might be expected, this growing use of an increasing amount of information content is supported by a number of communications, networks and systems. These many data transmission channels, along with their respective schemes and protocols, are always evolving in an attempt to provide faster and more reliable means of data communication.
The first communication channels for data transmission were, of course, wires and cables of a conducting material such as copper. Data transmission may occur through a dedicated line, or series of lines, extending from one computing device to another. Connection may also be made via a network such as the public-switched telephone network (PSTN) or, more recently, the Internet, where a circuit for communication may be set up as needed. Ad hoc communication circuits may be established using mechanical switches to connect existing lines. They may also be created logically using routers with software switches determining where certain information should be sent from a number of semi-permanently existing choices. The same principles may be used on a smaller scale, such as between offices of a particular office building, using a local area network (LAN).
Naturally, the data must be converted into a suitable form for transmission—encoded in some fashion recognizable to the intended recipient. There are many methods for doing so. In some systems, the data is organized into discreet units called packets, and each packet is individually transmitted. Each data packet must be separately addressed so that it can be routed to its destination by the most efficient route. Each packet must also contain identifying information so that the packets can be reassembled in the proper order at their destination. This extra information, required for transmission but then discarded, is sometimes referred to as “overhead”. Other types of overhead may include error-checking information, used in an error-checking algorithm at the receiver to determine if the packet has been correctly received. System design may include an acceptable error rate, this rate in part defining the quality of service (QoS) of the system. An increase in the acceptable error rate would normally be made to increase transmission speed. Different applications have different QoS requirements. Unsuccessfully transmitted packets may be retransmitted if the transmitting stations become aware of the transmission failure. Depending on the system's design, the receiver may send an acknowledgment message (ACK) to notify the transmitter that the data has been properly received, or send a negative acknowledgment message (NAK) if not. In some systems, both ACK and NAK messages may be used. Delay in the transmission of information is also an important factor in determining QoS. As described below, the present invention is directed at improving both of these QoS parameters.
A communication channel increasing in popularity is the wireless link, which is able to transmit data over an air interface using electromagnetic radiation in the radio frequency range. As with other links, these wireless channels are becoming more efficient and therefore more desirable. In addition, of course, a wireless link enables mobility. Sending and receiving stations are not confined to a fixed site or to a site with a wire-based network access. A cellular telephone network is one example of a system that transmits data over a wireless air interface. Note, however, that in such a network the path taken by transmitted data from source to destination is only in part an air interface. Wireless access in cellular networks is only used for subscribers to gain access to the network infrastructure.
Another example of a system using an air interface is a wireless local area network (WLAN). FIG. 1 is a simplified block diagram illustrating selected components of an exemplary WLAN 10. The WLAN 10 of FIG. 1 includes four stations, enumerated 1 through 4, and an access point 5. Each of the stations is operable to communicate with the access point over one or more radio-frequency links. The transmission channel from the access point 5 to one or more of the stations is typically referred to as the downlink, and transmissions in the other direction the uplink.
Note that in the configuration of FIG. 1, as with the cellular network referred to above, access point 5 is fixed and connected to a larger network, perhaps one that includes other access points. Such an application may be useful, for example, in a university where access points at various physical locations permit students and faculty to establish a network connection using wireless communication.
The set of stations shown in FIG. 1, which may vary in number, is sometimes referred to as a basic service set (BSS) and, including the access point 5, as an infrastructure BSS (If-BSS). A number of If-BSSs may be connected together to form an extended service set (ESS) (not shown). The network may even have the capability of “handing over” communications with a station from one access point to another, so that users may physically relocate during a communication session with little or no interruption. In addition to other If-BSSs, stations in WLAN 10 may also have access to larger central computers and more widespread networks, such as the Internet.
The WLAN of FIG. 1 is only exemplary, of course, and other network configurations are possible. Some networks may be set up on an ad hoc basis and establish communication between a number of nodes without a fixed (or pre-designated) access point. The stations may in some networks be operable to communicate directly with each other as network, and in such cases the access point may be is unnecessary. Such a network may be referred to as an independent BSS (IBSS). Yet another type of network is a mesh network, where various of the communication stations present may in a sense act as routers, allowing two or more stations to communicate (at lower power) through intermediaries rather than directly with each other. The present invention may be applied in any of these networks and the illustrations above are intended to be illustrative rather than limiting.
While the wireless air interface provides the advantage of mobility, it presents challenges in terms of increasing capacity without sacrificing QoS. By their nature, radio links may have a greater risk of signal distortion and lost data than a conductive wire or fiber-optic cable.
Nevertheless, as wireless communication grows in popularity, greater demands are being placed on the air interface. New techniques for more efficiently and reliably transmitting data are constantly in demand. The present invention provides such an improvement.